Dikerogammarus villosus, also known as the killer shrimp,[1][2] is a species of amphipodcrustacean native to the Ponto-Caspian region of eastern Europe, but which has become invasive across the western part of the continent. In the areas it has invaded, it lives in a wide range of habitats and will kill many other animals, often not eating them. It is fast-growing, reaching sexual maturity in 4–8 weeks. As it has moved through Europe it threatens other species and has already displaced native amphipods as well as other amphipods which had invaded areas previously.

Contents

D. villosus can grow up to 30 millimetres (1.2 in) in length, relatively large for a freshwater amphipod. It varies in appearance, with some specimens being striped, and some not. It has relatively large mandibles which allow it to be an effective predator.[2]

D. villosus can colonise many types of habitat as it is able to tolerate a wide range of temperatures (0–30 °C or 32–86 °F), low oxygen concentrations, and salinity up to 20‰. It is found in lakes, canals and rivers living in a range of substrates.[2] It is thought that zebra mussels change habitats by increasing the amount of benthic organic matter, which benefits D. villosus helping them to outcompete other species. When given a choice, D. villosus spend more time feeding around zebra mussel shells than a bare substrate.[1]

D. villosus breeds all year round so long as the water temperature is above 13 °C (55 °F). When they mate, the female is carried on the ventral side of the male. Each pair produces an average of 27 eggs, but up to 50 eggs can be laid. The young animals become sexually mature in 4 to 8 weeks, once they are 6 mm in length and after moulting several times. They are fast-growing, during winter increasing by 1.3–2.9 mm in length per month and by 2.0–2.6 mm every two weeks in spring. Populations are predominantly female.[2][5]

In the Netherlands, D. villosus is threatening the native amphipod species Gammarus duebeni, as well as Gammarus tigrinus which had previously become invasive after previously being introduced from North America.[9] It is thought to have displaced two other species of Dikerogammarus (D. bispinosus and D. haemobaphes) which were previously invasive in the Danube.[10] Its ability to attack and feed on a range of species could cause the local extinction of some species.[8]